On July 11, the James Webb Space Telescope (JWST) made history by releasing its debut image: a gem-filled photo that was touted as the deepest picture of the universe ever taken.
In addition, it looks further into space than any observatory before it James Webb Space Telescope has another trick in its mirrors: it can peer further into the past than any other telescope, observing distant stars and galaxies as they appeared 13.5 billion years ago, shortly after the beginning universe as we know it.
How is this possible? How can a machine look “into the past”? It’s not magic; it’s just the nature of light.
“Telescopes can be time machines. Looking into space is like looking back in time,” NASA scientists explained on WebbTelescope.org (opens in a new tab). “It sounds magical, but it’s actually very simple: Light needs time to travel through the vast expanses of space to reach us.”
All the light you see—from the twinkling of distant stars to the glow of a desk lamp a few feet away—takes time to reach your eyes. Fortunately, light travels incredibly fast – about 670 million miles per hour (1 billion kilometers per hour) – so you’d never notice it traveling from, say, a desk lamp to your eyes.
However, when you look at objects that are millions or billions of miles away – like most objects in the night sky – you see light that has traveled a long, long way to reach you.
Take it The sun, for example. Earth’s home star is an average of 93 million miles (150 million kilometers) away. This means that it takes about 8 minutes and 20 seconds for light to travel from the Sun to the Earth. So when you look at the sun (although you should never look directly at the sun (opens in a new tab)), you see it as it looked more than 8 minutes ago, not as it looks now—in other words, you’re looking 8 minutes into the past.
The the speed of light so important to astronomy that scientists prefer to use light years rather than miles or kilometers to measure great distances in space. One light year is the distance that light can travel in a year: approximately 5.88 trillion miles, or 9.46 trillion km. For example, North star, North staris about 323 light years away Earth. Every time you see this star, you are seeing light that is over 300 years old.
So you don’t even need a fancy telescope to peer into the past; you can do it with your own naked eyes. But to look really far into the past (say, to the beginning of the universe), astronomers need telescopes like JWST. Not only can JWST zoom in on distant galaxies to observe visible light coming from many millions of light-years away, but it can also pick up wavelengths of light invisible to the human eye, such as infrared waves.
Many things, including people, radiate heat as infrared energy. This energy cannot be seen with the naked eye. But when infrared waves are viewed with the right equipment, they can reveal some of the hardest-to-find objects in the universe. Because infrared radiation has a much longer wavelength than visible light, it can pass through the dense, dusty regions of space without being scattered or absorbed, in accordance with NASA (opens in a new tab). Many stars and galaxies that are too distant, faint, or obscured to be seen in visible light emit heat energy that can be defined as infrared radiation.
This is one of the most convenient tricks of JWST. Using infrared instruments, the telescope can peer into the dusty regions of space to study the light emitted more than 13 billion years ago by the oldest stars and galaxies in the universe.
This is how JWST took its famous image of the deep field, and this is how it will try to peer even further into the past, into the first few hundred million years (opens in a new tab) after Big explosion. The stars that the telescope will discover may actually be long dead, but as their ancient light makes a long journey across the universe, JWST offers our mortal eyes a one-of-a-kind display of time travel.
Originally published on Live Science.
https://www.space.com/james-webb-space-telescope-see-the-past/ Can James Webb’s telescope see the past?